The present application claims priority to Japanese Application No. P2000-042338 filed Feb. 21, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a semiconductor laser emitting apparatus. More particularly, the present invention is concerned with a semiconductor laser emitting apparatus which emits a laser beam in a multi-lateral mode, in which the near field pattern (hereinafter, frequently referred to simply as xe2x80x9cNFPxe2x80x9d) is stabilized.
2. Description of the Related Art
A conventional semiconductor laser emitting apparatus which emits a laser beam in a multi-lateral mode has, on an active layer, a cladding layer having a stripe structure such that the width is as large as 10 xcexcm or more (i.e., wide-stripe structure), and has a structure shown in FIG. 8.
As shown in FIG. 8, in a conventional semiconductor laser emitting apparatus 101 which emits a laser beam in a multi-lateral mode, a part of a cladding layer 112 formed on an active layer 111 is in a stripe form, and this stripe-form portion constitutes a current injection region 121. On both sides of the current injection region 121, current non-injection regions 122 having implanted thereinto, for example, boron ions (B+) are formed. The cladding layer 112 is formed so that the thickness t of the portions of the cladding layer 112 under the current non-injection regions 122 becomes 1 xcexcm or more, for example, about 1.3 xcexcm.
However, in the conventional semiconductor laser emitting apparatus which emits a laser beam in a multi-lateral mode, the NFP is unstable at a certain injection current value (output). This phenomenon is described below with reference to FIGS. 9A and 9B.
In a semiconductor laser emitting apparatus 101 shown in FIG. 9A, light portions L and dark portions D are formed in the NFP. As the injection current value (or an optical output) is changed, the light portions L are seen so that they fluctuate in the right and left directions (as indicated by arrows). Alternatively, a part of or a whole of the light portions and dark portions in the NFP is changed, so that, as shown in FIG. 9B, the semiconductor laser emitting apparatus 101 is in a state such that the light portions L and the dark portions D in the NFP are reversed. That is, the light portions L and the dark portions D irregularly change places with one another with a lapse of time. In addition, a change in the light emission strength is observed at the edge of the NFP. Thus, the NFP becomes unstable with time.
The above phenomenon in which the light and dark portions in the NFP fluctuate is a problem inherent in the multi-lateral-mode semiconductor laser emitting apparatus, and does not arise in the semiconductor laser emitting apparatus having a narrower stripe width (for example, about 3 xcexcm or less), i.e., the so-called single mode oscillation semiconductor laser emitting apparatus.
In addition, in a conventional semiconductor laser emitting apparatus having a gain waveguide structure, a difference in refractive index is not made between the portion directly under the portion in a stripe form and the outside thereof. Therefore, the NFP broadens also in the direction of the outside of the portion directly under the portion in a stripe form, so that there occurs the above phenomenon in which the NFP becomes unstable.
When the above semiconductor laser emitting apparatus is used in a machine required to achieve a uniformity of light emission, such as a printer, the phenomenon in which the NFP becomes unstable causes unevenness (for example, printing unevenness in a case of a printer). For obtaining the uniformity of light emission, there is a method in which an oscillated laser beam is once passed through an optical fiber so that it becomes uniform, and the resultant uniform laser beam is used. However, the use of this method disadvantageously causes an increase in cost.
Further, the current value at which the NFP becomes unstable varies depending on operation conditions, such as a temperature of the environment for operation, and, the semiconductor laser emitting apparatuses produced from the same materials under the same conditions respectively have different current values at which the phenomenon in which the NFP becomes unstable occurs. Therefore, it has been difficult to operate the semiconductor laser emitting apparatus while avoiding the operating point at which the NFP becomes unstable.
The present invention is a semiconductor laser emitting apparatus which has been made for solving the above-mentioned problems accompanying the conventional art.
The semiconductor laser emitting apparatus of the present invention emits a laser beam in a multi-lateral mode and comprises a cladding layer in a stripe form formed on an active layer, wherein a current injection region of the semiconductor laser emitting apparatus has a difference in optical absorption loss between the inside and the outside of the current injection region, wherein the cladding layer disposed on the outside of the current injection region is formed so as to have a thickness of 0.7 xcexcm or less. Alternatively, in the semiconductor laser emitting apparatus of the present invention, a current injection region has a difference in optical absorption loss between the inside and the outside of the current injection region, and the cladding layer is formed only in the current injection region.
In the semiconductor laser emitting apparatus of the present invention, the cladding layer disposed on the outside of the current injection region is formed so as to have a thickness of 0.7 xcexcm or less. Therefore, a current is efficiently injected into the current injection region, so that the current leakage amount is suppressed. Further, the current injection region of the semiconductor laser emitting apparatus has a difference in optical absorption loss between the inside and the outside of the current injection region. Therefore, the waveguide of a laser can be changed between the inside and the outside of the current injection region in a stripe form, so that the laser is efficiently kept directly under the portion in a stripe form, thus making it possible to obtain a stable NFP free of fluctuation in the light portions and the dark portions therein.
As mentioned above, in the semiconductor laser emitting apparatus of the present invention, the cladding layer disposed on the outside of the current injection region is formed so as to have a thickness of 0.7 xcexcm or less, or the cladding layer is formed only in the current injection region. Therefore, the current leakage amount can be suppressed, making it possible to efficiently inject a current into the current injection region. In addition, the current injection region of the semiconductor laser emitting apparatus has a difference in optical absorption loss between the inside and the outside of the current injection region. Therefore, the waveguide of a laser can be changed between the inside and the outside of the current injection region in a stripe form, so that the laser is efficiently kept directly under the portion in a stripe form, rendering it possible to obtain a stable NFP without problems of a change with time in the light emission pattern, a change in the strength at an edge of the NFP, and the like caused by the changing of the optical output or current injection amount, which problems have been inevitably encountered in the conventional semiconductor laser emitting apparatus which emits a laser beam in a multi-lateral mode.
Thus, the semiconductor laser emitting apparatus which emits a laser beam in a multi-lateral mode can be applied to the fields which are required to achieve a uniformity of light emission. Further, the uniformity of light emission can be achieved without using an optical fiber, and hence, an increase in cost can be prevented.